Acrylate copolymers containing epoxide groups and their use as binding agents in powder coatings are already known: See, for example, United States patents: U.S. Pat. No. 3,781,379, U.S. Pat. No. 4,042,645 and U.S. Pat. No. 4,346,144(incorporated herein by reference). As far as the hardeners are concerned, use can be made in this connection of polybasic acids or, preferably, dibasic acids, and their anhydrides or substances that form a dibasic acid under the conditions that prevail during hardening. In principle, use can also be made of other carboxy-functional compounds as hardeners such as, for example, amorphous and/or semi-crystalline polyester resins and/or acrylate resins with free carboxy groups.
The copolymers that are described in the aforementioned patents all contain glycidyl acrylate, or, as the case may be glycidyl methacrylate. The rest of the copolymer consists of other unsaturated monomers, i.e., one is dealing here with acrylate copolymers that contain glycidyl esters. The preparation of monomeric glycidyl (meth)acrylate is not simple from a technical standpoint since glycidyl (meth)acrylate readily polymerizes, and the isolation of the pure monomer is very problematical. In addition to the short storage stability of glycidyl (meth)acrylate, its high toxicity also presents problems during processing. Thus the preparation of acrylate polymers that contain glycidyl esters via the copolymerization of glycidyl (meth)acrylate is problematical and not recommended. A further disadvantage of this process is that water cannot be used as the-reaction medium.
U.S. Pat. No. 3,294,769 (incorporated herein by reference) describes, in general, a process for the preparation of acrylate polymers that contain glycidyl ester groups via the reaction of carboxy-functional acrylate polymers with epichlorohydrin.
The saponification of methyl methacrylate polymers and their subsequent reaction with epichlorohydrin has been investigated by Sandner et al. (see, Angew. Makromol. Chem., 181: 171-182(1990) and Makromol. Chem., 192: 762-777(1991)).